The present invention relates generally to a new and improved pipe fitting and method for making same, and more particularly, to a prefabricated, butt-welded double containment pipe fitting.
There is an ever increasing concern today over the environment and particularly to chemical spills and leaks where chemicals are absorbed by the ground and migrate to groundwater. The cleanup of such chemical spills is both costly and tedious. In order to provide some measure of assurance against chemical contamination, the chemical industry, especially the chemical waste processing industry, has adopted the use of double containment pipe and underground storage tanks to convey and store fluid chemicals.
Double containment piping consists of two pipes. Both pipes are typically made of a thermoplastic material because of the high corrosion resistance, low weight and low cost of plastics in general. One pipe of the two pipes is known as the primary pipe and is intended to convey chemical fluids or effluents. The other pipe is known as a secondary pipe and it extends around the primary pipe in a spaced-apart relationship to define an annular space between the primary and secondary pipes. The secondary pipe provides a protective casing or containment which will contain chemicals escaping from the primary pipe due to leakage and prevent the chemicals from escaping into the environment. Leak detection or monitoring systems may be disposed within the annular space for identifying leaks to the system processing operator.
Prior double containment piping systems were costly and labor-intensive. Double containment piping systems typically required the installation contractor to fabricate much of the system during its installation. This fabrication typically included the fabrication of various fittings such as wye, lateral, tee and reducing fittings. Certain other fittings also were field-fabricated such as elbows and cross fittings. This field fabrication was a costly aspect to any double containment piping system installation. The field fabrication of such fittings was expensive because it required cutting pipe lengths, or spools to obtain various size pipe portions which were then fillet welded together using a thermoplastic welding rod. This process is both time consuming to the contractor and the owner and the quality effected in the field may not be up to the standards of quality that can be readily replicated in a factory situation.
Although some past methods have been known for joining together thermoplastic pipe sections, each method has certain disadvantages. For example, U.S. Pat. No. 3,013,925 issued Apr. 3, 1959 describes a method in which two pipe spools are held together in a vise and their opposing ends are brought into contact with a planar heating element to melt the endwalls of the pipe sections. After heating, the pipe endwalls were brought together and held in place until the plastic cools. This method is only effective for joining straight pipe lengths.
U.S. Pat. No. 4,779,652, issued Oct. 25, 1988, describes a integrally molded pipe fitting which a primary and secondary pipes are molded together as one piece and are separate by integral pipe supports molded integrally therewith. Molding the primary and secondary pipe together as a single unit requires a costly investment in molds and this investment may limit the ability of the pipe supplier to supply prefabricated custom fittings in accordance with a contractor's installation drawings. A mold must be made for each particular style fitting and thereby reduces the likelihood of a cost effective custom fitting being made quickly.
U.S. Pat. No. 5,185,049 which issued Feb. 9, 1993, describes an apparatus for butt-welding double containment pipe sections together by bringing opposing endwalls of the pipes in contact with a hinged planar heating element until the plastic softens, at which time the ends are joined together to form a solid butt-joint. The planar nature of this heating element precludes its use for assembly of complex fittings such as tee, wye, cross or reducing fittings which require detailed calculation of angled mating surfaces.
In order to reduce the amount of labor expended in construction of double containment pipe systems and thereby lower the overall cost to the system, a need therefore exists for prefabricated pipe fittings, wherein the pipe fittings components are butt-welded together, thereby permitting complex fittings to be fabricated as modular components of either standard size or custom size of an overall double containment piping system.